linux-kernel - Re: [PATCH v5 23/23] KVM: arm64: GICv4.1: Expose HW-based SGIs in debugfs

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Message-ID: <8d7fdb7f-7a21-da22-52a2-51ee8ac9393f@huawei.com>
Date:   Fri, 20 Mar 2020 19:35:39 +0800
From:   Zenghui Yu <yuzenghui@...wei.com>
To:     Marc Zyngier <maz@...nel.org>
CC:     Auger Eric <eric.auger@...hat.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <kvmarm@...ts.cs.columbia.edu>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Jason Cooper <jason@...edaemon.net>,
        "Robert Richter" <rrichter@...vell.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "James Morse" <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>
Subject: Re: [PATCH v5 23/23] KVM: arm64: GICv4.1: Expose HW-based SGIs in
 debugfs

Hi Marc,

On 2020/3/20 17:09, Marc Zyngier wrote:
> Hi Zenghui,
> 
> On 2020-03-20 04:38, Zenghui Yu wrote:
>> Hi Marc,
>>
>> On 2020/3/19 23:21, Marc Zyngier wrote:
>>> With GICv4.1, you can introspect the HW state for SGIs. You can also
>>> look at the vLPI state by peeking at the virtual pending table, but
>>> you'd need to unmap the VPE first,
>>
>> Out of curiosity, could you please point me to the "unmap the VPE"
>> requirement in the v4.1 spec? I'd like to have a look.
> 
> Sure. See IHI0069F, 5.3.19 (VMAPP GICv4.1), "Caching of virtual LPI data
> structures", and the bit that says:
> 
> "A VMAPP with {V,Alloc}=={0,1} cleans and invalidates any caching of the
> Virtual Pending Table and Virtual Configuration Table associated with the
> vPEID held in the GIC"
> 
> which is what was crucially missing from the GICv4.0 spec (it doesn't say
> when the GIC is done writing to memory).

OK. Thanks for the pointer!

> 
> Side note: it'd be good to know what the rules are for your own GICv4
> implementations, so that we can at least make sure the current code is 
> safe.

As far as I know, there will be some clean and invalidate operations
when v4.0 VPENDBASER.Valid gets programmed. But not sure about behaviors
on VMAPP (unmap), it may be a totally v4.1 stuff. I'll have a talk with
our SOC team.

But how can the current code be unsafe? Is anywhere in the current code
will peek/poke the vpt (whilst GIC continues writing things into it)?


Thanks,
Zenghui